Study On Treatment Of Food-processing Wastewater By Anoxia/Two-Stage Biological Contact Oxidation Process

Food processing wastewater, with the characteristics of innocuity, high biodegradability, changeable pH, water quality and water flow, containing lots of floating solids, organic matters, grease, nitrogen and phosphorus, is one of the main sources of polluting natural water. However, present treatment facilities of food processing wastewater have the disadvantages of high investment and operating cost, complicated maintenance and management, low stability and efficiency, abundant residual activated sludge, frequent sludge bulking, the concentration of CODcr and NH3-N in effluent not up to the standard. Therefore, research and development of a set of wastewater disposal process for food processing wastewater with advanced technology, high efficiency, economy and practicability, simple operation, is imperative. In this experiment, food processing wastewater is treated with anoxia/two-stage bio-contact oxidation process. As a result, the pilot study shows that it is feasible to treat food processing wastewater with anoxia/two-stage bio-contact oxidation process.According to the characteristics of food processing wastewater, firstly, the experiment discusses the laws of activated sludge and biofilm growth and the suitable cultivation conditions of biofilm during the biofilm colonization in the reactor; secondly, the experiment inspects the influence of hydraulic retention time (HRT), gas-water ratio (GWR), aeration distribution ratio (ADR) and mixed liquor reflux ratio (MLRR) on the treatment of food processing wastewater by anoxia/two-stage bio-contact oxidation process respectively; finally, the optimal process parameters of the treatment of food processing wastewater by anoxia/two-stage bio-contact oxidation process are ascertained, and then the effect of treatment in optimal conditions is discussed. The experiment results show that:microorganisms in the activated sludge and biofilm live under the growth laws of adaptive phase, growing phase, and again, and stationary phase in sequence; in the conditions of adequate nutrition and appropriate nutrition proportion, lower GWR, suitable temperature and pH are helpful to shorten the growth phase and increase efficiency of biofilm colonization; the optimal HRT, GWR, ADR, MLRR of the treatment of food processing wastewater by anoxia/two-stage bio-contact oxidation process are respectively 7h, 15:1, 2:1, 3:1.On the optimal conditions that HRT, GWR, ADR, MLRR are 7h, 15:1, 2:1, 3:1 respectively, the effect of the treatment of food processing wastewater by anoxia/two-stage bio-contact oxidation process is perfect, when the average removal rate of CODcr and NH3-N respectively comes up to 92.4% and 80.7% and the system is stable and reliable.This experimental research shows that:the water quality of the effluent of the treatment of food processing wastewater by anoxia/two-stage bio-contact oxidation process could meet the state's first-level standard for wastewater discharge (GB8978-1996), in which the concentration of CODcr and NH3-N is respectively less than 100mg/L and 15mg/L; this process with advanced technology, high efficiency, great economy, practicability and feasibility, a biological treatment technique for food processing wastewater , is worthy of application and dissemination.